The invention relates to improvements in bookbinding machines in general, and more particularly to improvements in bookbinding machines of the type known as perfect binders wherein the backs and certain other portions of stacks of paper sheets are coated with adhesive prior to attachment of covers. Such machines can be utilized for mass production of books (e.g., soft cover books), brochures, pamphlets and similar printed products.
It is already known to provide a perfect binder with a transporting unit having a set of grippers or tongs which can be closed to engage discrete stacks of sheets at a receiving location and to thereupon advance the engaged stacks past several successive treating stations (where various tools treat selected portions of the stacks, particularly those portions which extend downwardly beyond the undersides of the respective grippers) and on to a removing or withdrawing location. The undersides of all grippers in the path between the receiving and removing locations can be disposed in a common plane. It is further known to provide such perfect binders with mechanisms which can individually adjust the distance of each treating tool from the common plane of the undersides of the grippers. This is desirable and advantageous because the treatment at one or more stations can be intensified, eliminated or otherwise altered, depending on the nature of the conveyed material and upon the desired quality of books, brochures or pamphlets (hereinafter referred to as books for short).
An important characteristic of a finished stack which is ready to be connected with a cover is the extent to which the back of the book (i.e., the lowermost portion of the stack between the jaws of a gripper) extends downwardly beyond the underside of the respective gripper. The extent to which the lowermost portion of a stack which is ready to be adhesively connected with a cover projects beyond the underside of the corresponding gripper can be altered by adjusting the level or levels of grinding, milling and/or other material removing tools which are installed beneath the path of the grippers between the receiving and removing locations. In many instances, the height of the lower portion of a stack beneath its gripper will depend on the nature of the covers which are to be applied to the treated and adhesive-coated stacks. Thus, the extent to which a stack projects downwardly beyond the underside of the respective gripper will determine the width of the layers of adhesive which can be applied to portions of the two major sides of a treated stack if a cover is to adhere to the back as well as to adjacent portions of major sides of the stack of paper sheets in a finished book.
The person in charge of setting up a perfect binder seeks to shorten that portion of a stack which extends downwardly beyond the corresponding gripper because the treatment of stacks is more difficult if the trimming, milling, grinding and/or other tools are required to remove a relatively large quantity of paper at the underside of the path of movement of the grippers. In fact, once the height of the downwardly projecting portion of a stack reaches a certain value, the tools at the underside of the path for the stacks and for their grippers are incapable of removing all of the material or can remove the material at the expense of the appearance (quality) of the finished printed products.
In order to facilitate the task of a person in charge of setting up a perfect binder, the machine is equipped with various gauges or other indicating instruments which render it possible to ascertain the positions of various tools relative to the common plane of the undersides of the grippers for discrete stacks. Individual adjustment of each treating tool relative to the aforementioned plane is a time-consuming operation and affects the output of the perfect binder if the machine is to be set up in a different way at frequent intervals.
A drawback of presently known perfect binders is that the instruments which indicate the positions of various treating tools relative to the common plane of the undersides of grippers for discrete stacks of printed sheets do not furnish direct indications of several parameters which are important in order to properly set up the binder for a particular bookbinding operation. More particularly, the presently utilized instruments do not indicate the actual positions of the respective treating tools relative to the downwardly projecting portions of stacks of paper sheets in the grippers. Moreover, such instruments do not directly indicate the levels of the respective treating tools with reference to the levels of other treating tools. For example, if the height or length of the downwardly projecting (exposed) lower portion of a stack exceeds the standard height by 3 mm, the indicator which is associated with a customary roller-shaped adhesive applicator indicates 4 mm even though the thickness of the adhesive layer which is applied to the exposed lower portion of a stack is only 1 mm. The situation is analogous as concerns the information which is furnished by the indicators cooperating with other treating tools beneath the path of movement of the grippers and stacks from the receiving location to the removing location of a standard perfect binder. Therefore, the person in charge must waste considerable time to calculate the relative positions of the treating tools and the positions of such tools relative to the common plane of the undersides of grippers prior to starting with, or in the course of, a change of setup. A single relatively minor error can necessitate the ejection of a large number of unacceptable printed products. As a rule, final adjustments are made during a test run which involves the production of a large number of unacceptable books because the person in charge of altering the setup must examine the quality of finished products prior to repeatedly adjusting one or more treating tools in order to eliminate defects or to improve the quality of the books so that it meets the prescribed norm.